This invention relates generally to the field of data storage devices, and more particularly, but not by way of limitation, to the relation of rotational vibration stimuli to the performance of hard disc drives.
Disc drives are used for data storage in modern electronic products ranging from digital cameras to computer systems and networks. Typically, a disc drive includes a mechanical portion, or head disc assembly (also referred to as an HDA), and electronics in the form of a printed circuit board assembly (PCB), mounted to an outer surface of the head disc assembly. The PCB controls the HDA functions and provides an interface between the disc drive and its host.
Generally, a head disc assembly comprises one or more magnetic discs affixed to a spindle motor assembly for rotation at a constant speed, an actuator assembly supporting an array of read/write heads that traverse generally concentric data tracks radially spaced across the disc surfaces and a voice coil motor providing rotational motion to the actuator assembly. The continued demand for disc drives with improved reliability and operating efficiencies has caused disc drive manufacturers to seek ways to increase the ability of disc drives to operate in the presence of rotational vibration stimuli, while simultaneously reducing the exposure of the disc drive to rotational vibration during execution of data transfer functions.
Disc drives can suffer degraded data throughput performance and reduced data integrity from exposure to rotational vibration stimuli. A disc drive is most susceptible to rotational vibration stimuli because of the rotary actuator positioning system. The more rotational vibration stimuli present in the disc drive""s operational environment, the harder it is for the actuator to track, follow and seek settle. One of the primary generators of rotational vibration stimuli is the actuator itself. As the actuator accelerates/decelerates, the base plate has an equal and opposite reaction torque. It is this reaction torque that can be amplified by the mechanical mounting environment of a disc drive, such as a chassis supporting the disc drive. Amplification of the reaction torque can affect the operating performance of the source disc drive and can even affect the operating performance of adjacent disc drives secured within the same mechanical mounting environment.
High rotational vibration (RV) levels can occur in the chassis of disc drive array systems, mass storage units, desktop systems and notebook computers. Disc drive design options available to disc drive designers, for reducing sensitivity to rotational vibrations, are predominantly limited to improvements in the servo system of the disc drive. Within the servo system, the areas generally available to the disc drive designer for enhancements that reduce the disc drive""s sensitivity to rotational vibration are incorporation of compensation algorithms and faster processors for shorter recovery times from a rotational vibration stimuli event.
Chassis designers generally have more options available to them for reducing or suppressing rotational vibrations transferred from the chassis to the disc drive than disc drive designers have in dealing with rotational vibrations transferred into the disc drive from the chassis. Specifically, chassis designers can move the response frequency of the chassis through mechanical tuning techniques. Such techniques include altering a configuration of support members of the chassis, changing the mass of the chassis through addition or removal of material, selecting alternate materials and through mechanical dampening techniques such as the use of constrained layer dampening between members of the chassis. Working together, disc drive designers and chassis designers can successfully deal with the potential rotational vibration problem.
While there are other testing methods that allow for monitoring vibration of various devices, a method for constantly monitoring multiple disc drives during rotational vibration testing and condensing, into a single index, frequency domain data collected during that testing is currently unavailable. Provision of a single index, for comparison against a predetermined value, would be useful in helping disc drive designers and chassis designers focus on developing optimum solutions to rotational vibration stimuli experienced by disc drive. A single index would also aid in monitoring and verifying the effects of changes, made to either the disc drive or the mechanical mounting environment, relative to the level of rotational vibration stimuli experienced by the disc drive mounted in the particular mechanical mounting environment resulting from the change.
Therefore, challenges remain and a need persists for techniques that relate overall energy and frequency content of rotational vibration stimuli experienced by the mechanical mounting environment of the disc drive with measured performance of the disc drive. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.
The present invention provides an apparatus and associated method for relating rotational vibration stimuli of a mechanical mounting environment to performance of a disc drive and includes selecting a sample disc drive of a drive species and mounting the sample disc drive within a selected mechanical mounting environment; attaching an accelerometer to the sample disc drive for measuring rotational vibration; inducing a predetermined rotational vibration stimuli into the mechanical mounting; collecting vibration data with the accelerometer for use in determining a rotational vibration index for the mechanical mounting environment with the selected disc drive mounted into the mechanical mounting environment; providing a predetermined rotational vibration index for the drive species for comparison with the determined rotational vibration index; and comparing the rotational vibration index calculated for the mechanical mounting environment with the rotational vibration index of the drive species to relate the rotational vibration stimuli of the mechanical mounting environment to the performance of the sample disc drive.
Additionally, the apparatus and associated method provides a test system for predicting performance of a disc drive of a drive species mounted in a mechanical mounting environment. The test system includes a pair of accelerometers attached to the disc drive for measuring response of the disc drive to a rotational vibration stimulus. Communicating with the accelerometers is a computer with a data acquisition card for acquiring and analyzing the response of the disc drive to the rotational vibration stimuli. The test system also includes a storage device communicating with the computer for saving measurements made by the accelerometers measuring the response of the disc drive to the rotational vibration stimuli imparted on the mechanical mounting environment. The test system further includes software incorporating a rotational vibration index function programmed into the computer and communicating with the data acquisition card to compute the rotational vibration index for the mechanical mounting environment with the disc drive mounted to the mechanical environment.